Field of the Invention
The invention relates to an induced draft fan.
Description of the Related Art
A typical induced draft fan system, as shown in FIG. 1, includes: a housing A, a wind wheel, and an AC motor B. The housing A is provided with an air inlet, an air outlet, and an inner cavity for accommodating the wind wheel. The air inlet and the air outlet communicate with the inner cavity. The AC motor B is disposed on the housing A. A front end part of a rotating shaft of the AC motor B protrudes inside the inner cavity and is connected to the wind wheel. An air switch C (a negative pressure switch for measuring the air pressure inside the inner cavity) is mounted on the housing A for detecting whether the induced draft fan is started. Such an induced draft fan system utilizes the air switch to measure the pressure therein to conduct the starting and closing movements. The air switch, however, is easily influenced by multiple factors and thus has a very large control error, thereby resulting in equipment failures and security risk.